Measurement of – induced single leptons in the HADES RICH

T. Eberl, TU München

T. Eberl, T. Christ, L. Fabbietti, J. Friese, R. Gernhäuser, J. Homolka, H.-J. Körner, M. Münch, B. Sailer, and S. Winklerfor the HADES collaboration

Motivation:• Study of close e+e- - pairs• RICH ring properties• Comb. backgr. in e+e- - spectroscopy

Exp. SetupHADES with low B-Field

Results• Opening angle distributions of identified close e+e- - pairs

• Properties of Cherenkov Rings !!!

Dilepton Spectroscopy

T. Eberl, TU München

Comb. Backgr.Suppression

Close pair recognition !!!! & rejection

2 close rings in RICH

2 close tracks in MDC

HADES : Low mass e+e- pairs from , p, A + A collisions

full scale HGEANT simulation

Sources of Close Rings & Tracks

T. Eberl, TU München

Possible combinations P1 P2 RICH MDC e+ e- 1 1e+ e- 1 2e+ e- 2 2e+ e- 2 1 fake ? e+ e- 2 3 ??...........

e+/- 1 1p 1 1 fake !+/- 1 1 fake !...........

rare cases :p e+/- 1 2 +/- e+/- 1 2...........

e+

e-

< > ~ 2 0

Conversionin

Target & Radiator

e+

e-

0

< > ~ 13 0

Dalitz

interestingpair ???

Physics processes :0 - Dalitz , conversion, compt. scatt.

e-

Experimental Setup @ GSI, Darmstadt

T. Eberl, TU München

HADES with RICH, MDC 1 / 2 , META , low B – field

optimized for e+/- with low p full reconstr. of low mass pairs

Deflection in B - fieldMDC–META

~ 1 / P

standard

Acceptance for -Dalitz leptons

T. Eberl, TU München

Simulation: -Dalitz decay

3-threshold of RICH

HADES acceptance

C + C @ E = 1A GeV

T. Eberl, TU München

Numerical Experiment(Simulation)UrQMD + HGEANTSetup as in exp.Trig: MMeta > 3; included

NNsimsim = = 77 * 10 * 1066 evts. evts.

Experiment @ SIS - GSI

Ibeam = 106 / s, Targ: tot = 5% Trig: MMeta > 3; /tot ~ 0,7

NNexpexp = = 99 * 10 * 1066 evts. evts.

Analysis conditions:Event selection:• MDC I/II : multiplicity Mtrack > 3• RICH : min. 1 Ring corr. with MDC & META

Hit matching conditions:• before B- field : MDC-RICHMDC-RICH• after B- field : MDC-META noMDC-META• no TOF cut !!

e+/e- cand. for C + C @ 1A GeV

T. Eberl, TU München

Rings in RICH

Defl. angles MDC–META

of reconstructed tracks in RICH & MDC & META

Single ??

Doublee+e-

-10 -8 -6 -4 -2 02 46 81 0

200

600

1000

1400

1800

2200 SIM

EXP

N = 89205

- [°]MDC META

Measured RICH Rings

T. Eberl, TU München

C + CE = 1A GeV

-Dalitz decay leptons ?!

Ring recognition:

Pattern Matrix

Hough-Transf.

e+ e- pairs

T. Eberl, TU München

Opening angle distr. in MDC (before B – field)Reasonable agreement !!!

C + CE = 1A GeV

Sim. normalised to Exp.

0 – Dalitz

Opening angle [deg]

Co

un

ts [

a.u

. ]

Sim (total)

Exp

Conversion

Ring selection for single electrons

T. Eberl, TU München

opening angle [°]

0

20

40

60

80

100

120

140

160

180EXP

SIM

0 8642 10

e+e- pairs with 1 track / ring

2 RICH rings2 RICH rings

2 MDC tracks2 MDC tracks

ee++

ee--

Opening angle distr.In MDC (before B - field)

Single rings !

Rings for close tracks

T. Eberl, TU München

opening angle [°]

0

50

100

150

200

250

300

350

400

EXP

SIM

0 8642 10

Opening angle distr.in MDC (before B - field) e+e- pairs with 2 tracks / ring

ee++ ee--

ee++ ee--

1 RICH 1 RICH ringring

2 MDC 2 MDC trackstracks

1 MDC 1 MDC tracktrack

Double rings !

Ring properties: charge & pads

T. Eberl, TU München

Charge/ring [a.u.] Pads/ring

Co

un

ts [

a.u

.]

Co

un

t s [

a.u

.]C

ou

nt s

[a

.u.]

Co

un

t s [

a.u

.]

SimExp

Charge per ring Pads per ring

single

double

C + CE = 1A GeV

single

double

ee++ee--

ee++ ee--

Ring properties: cluster & quality

T. Eberl, TU München

clusters/ring matrix sum [a.u.]

Co

un

ts [

a.u

.]

Co

un

t s [

a.u

.]C

ou

nt s

[a

.u.]

Co

un

t s [

a.u

.]

SimExp

Clusters per ring Pattern Matrix sum

C + CE = 1A GeV

single single

double double

ee++ee--

ee++ ee--

Lepton recognition

T. Eberl, TU München

HADES reconstruction probability for a -Dalitz decay lepton

C+C, E=1AGeV, low field setup, cons. param. set Momentum [MeV/c]

Po

lar

ang

le [

deg

]

GEANT Simulation:

-Dalitz decay

ee--

RICHRICHMDCMDC

METAMETA

ee++

RICHRICH

MDCMDCMETAMETA

min 1 lepton required !

Pair recognition

T. Eberl, TU München

Po

lar

ang

le [

deg

]

Momentum [MeV/c]

GEANT Simulation:

-Dalitz decay

HADES reconstruction probability for a lepton from an identified -Dalitz lepton pair

C+C, E=1AGeV, low field setup

ee--

RICHRICHMDCMDC

METAMETA

ee++

RICHRICH

MDCMDCMETAMETA

2 leptons required !

Summary

Dilepton spectroscopy with HADES :• Measurement of close pairs for low momentum e+e- • Good statistics of 0 – Dalitz and conversion leptons• Experimental data for comb. backgr. and eff. studies

Results from prel. analysis• Ident. of rings from fully reconstr. single leptons in RICH• Full scale simulation vs. experiment : ok• Simulation: single lepton reconstr. prob. for 0 – Dalitz • Meas. of key ring prop. for singles and doubles (for each sector)Outlook:• Quantitative comb. backgr. studies• Efficiencies for single lepton identification

T. Eberl, TU München